Impurity Control For A High Pressure CO2 Purification And Supply System

ABSTRACT

An apparatus for producing a purified, pressurized liquid carbon dioxide stream includes a distillation column (B) having packing (C) therein and a sump (D) below the packing, the distillation column in fluid communication with the liquid carbon dioxide supply tank for receiving the liquid carbon dioxide stream and the packing stripping volatile impurities from the liquid carbon dioxide stream; a heater (E) in contact with the liquid carbon dioxide stream in the sump (D) for vaporizing the liquid carbon dioxide stream in the sump; a vent in the distillation column (B) from which a first vaporized portion (G) of carbon dioxide vapor in the sump (D) is withdrawn from the distillation column: and a conduit (I) in fluid communication with the sump (D) and from which a second vaporized portion (H) of the carbon dioxide vapor in the sump is withdrawn into the conduit (I) to be introduced into the carbon dioxide vapor feed stream.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for reducingimpurities in a purified and pressurized liquid carbon dioxide stream.

Highly pressurized, purified liquid carbon dioxide is required for avariety of industrial processes. Such highly pressurized liquid isproduced by purifying industrial grade liquid carbon dioxide that isavailable at about 13 to 23 bar (1.3 to 2.3 MPa) and then pumping the Iquid to a pressure of anywhere from between about 20 and about 68 bar (2to 6.8 MPa). The problem with pumping, however, is that impurities suchas particulates or hydrocarbons can be introduced into the productstream as a byproduct of mechanical pump operation.

U.S. Pat. No. 6,327,872 discloses a method and apparatus for producing apressurized high purity liquid carbon dioxide stream in which a feedstream composed of carbon dioxide vapor is purified within a purifyingfilter and then condensed within a condenser. The resulting liquid isthen alternatively introduced and dispensed from two first and secondpressure accumulation chambers on a continuous basis, in which one ofthe first and second pressure accumulation chambers acts in a dispensingrole while the other is being filled.

High purity CO₂ can be used for the cleaning of optical components usingthe solvation and momentum transfer effects of CO₂ when sprayed onto theoptics. These benefits are achieved only if the purity of the CO₂ isvery high and the CO₂ is delivered at a high pressure.

SUMMARY

The present invention relates to a method (process) and apparatus forcontrolling and improving the purity of a pressurized liquid carbondioxide stream in which a feed stream composed of carbon dioxide vaporis condensed into a liquid that is subsequently pressurized, such as bybeing heated within a chamber.

A process embodiment of the present invention calls for in a batchprocess for producing a purified, pressurized liquid carbon dioxidestream including providing a liquid carbon dioxide supply (10),introducing a carbon dioxide vapor feed stream into at least onepurifying filter (13,14), condensing the purified vapor feed streamwithin a condenser (18) to form an intermediate liquid carbon dioxidestream, accumulating the intermediate liquid carbon dioxide stream in areceiver (20), introducing the intermediate liquid carbon dioxide streaminto at least on high-pressure accumulation chamber (30), heating thehigh pressure accumulation chamber (30) to pressurize the intermediateliquid carbon dioxide stream contained therein to a delivery pressure,delivering a pressurized liquid carbon dioxide stream from thehigh-pressure accumulation chamber (30), and discontinuing delivery ofthe pressurized liquid carbon dioxide stream for replenishing the highpressure accumulation chamber (30), wherein the improvement comprises:

-   -   withdrawing a liquid carbon dioxide stream (A) from the liquid        carbon dioxide supply (10);    -   introducing the liquid carbon dioxide stream (A) into a        distillation column (B) having packing (C) therein, and        stripping volatile impurities from the liquid carbon dioxide        stream with the packing;    -   vaporizing the liquid carbon dioxide stream (A) in a sump (D) of        the distillation column (B) for providing a carbon dioxide        vapor;    -   withdrawing from a vaporized portion (F) of carbon dioxide vapor        in the sump (D) a first vapor stream (G) vented from the        distillation column (B);    -   withdrawing from the vaporized portion (F) of the carbon dioxide        vapor in the sump (D) a second vapor portion (H) vented from the        sump into a conduit (I); and    -   introducing the second vapor portion (H) in the conduit (I) into        the carbon dioxide vapor feed stream upstream of the at least        one purifying filter (13,14).

Still another process embodiment of the present invention calls for abatch process for producing a purified, pressurized liquid carbondioxide stream, comprising: withdrawing a liquid carbon dioxide stream(A) from a liquid carbon dioxide supply (10); introducing the liquidcarbon dioxide stream (A) into a distillation column (B) having packing(C) therein, and stripping volatile impurities from the liquid carbondioxide stream with the packing; vaporizing the liquid carbon dioxidestream (A) in a sump (D) of the distillation column (B) for providing acarbon dioxide vapor; withdrawing from a vaporized portion (F) of carbondioxide vapor in the sump (D) a first vapor stream (G) vented from thedistillation column (B); withdrawing from the vaporized portion (F) ofthe carbon dioxide vapor in the sump (D) a second vapor portion (H)vented from the sump into a conduit (I); and introducing the secondvapor portion (H) in the conduit (I) into a carbon dioxide vapor feedstream.

Still another process embodiment of the present invention calls for in abatch process for producing a purified, pressurized liquid carbondioxide stream including distilling a feed stream including carbondioxide vapor off a liquid carbon dioxide supply (10), introducing thecarbon dioxide vapor feed stream into at least one purifying filter(13,14), condensing the purified carbon dioxide vapor feed stream withina condenser (18) to form an intermediate liquid carbon dioxide stream,accumulating the intermediate liquid carbon dioxide stream in a receiver(20), introducing the intermediate liquid carbon dioxide stream from thereceiver (20) into at least on high-pressure accumulation chamber (30),heating the high pressure accumulation chamber (30) to pressurize theintermediate liquid carbon dioxide stream contained therein to adelivery pressure, delivering a pressurized liquid carbon dioxide streamfrom the high-pressure accumulation chamber (30), and discontinuingdelivery of the pressurized liquid carbon dioxide stream forreplenishing the high pressure accumulation chamber (30), wherein theimprovement comprises:

-   -   introducing the carbon dioxide vapor feed stream (L) into a        distillation column (M) having packing (N) therein;    -   condensing a first portion (O) of the carbon dioxide vapor feed        stream (L) within a condenser (18) in fluid communication with        the distillation column (M) to form another intermediate liquid        carbon dioxide stream (T) and a liquid vent stream (Q); and    -   introducing the another intermediate liquid carbon dioxide        stream (T) into the receiver (20), and venting the liquid vent        stream (Q) from a bottom of the distillation column (M).

Still another process embodiment of the present invention calls for abatch process for producing a purified, pressurized liquid carbondioxide stream, comprising: introducing a carbon dioxide vapor feedstream (L) into a distillation column (M) having packing (N) therein;condensing a first portion (O) of the carbon dioxide vapor feed stream(L) within a condenser (18) in fluid communication with the distillationcolumn (M) to form an intermediate liquid carbon dioxide stream (T) anda liquid vent stream (Q); and introducing the intermediate liquid carbondioxide stream (T) into receiver (20), and venting the liquid ventstream (Q) from a bottom of the distillation column (M).

Still another process embodiment of the present invention calls for in abatch process for producing a purified, pressurized liquid carbondioxide stream including providing a liquid carbon dioxide supply (10),introducing a carbon dioxide vapor feed stream into at least onepurifying filter (13,14), condensing the purified vapor feed streamwithin a condenser (18) to form an intermediate liquid carbon dioxidestream, accumulating the intermediate liquid carbon dioxide stream in areceiver (20), introducing the intermediate liquid carbon dioxide streaminto at least on high-pressure accumulation chamber (30), heating thehigh pressure accumulation chamber (30) to pressurize the intermediateliquid carbon dioxide stream contained therein to a delivery pressure,delivering a pressurized liquid carbon dioxide stream from thehigh-pressure accumulation chamber (30), and discontinuing delivery ofthe pressurized liquid carbon dioxide stream for replenishing the highpressure accumulation chamber (30), wherein the improvement comprises:

-   -   withdrawing a liquid carbon dioxide stream (A) from the liquid        carbon dioxide supply (10);    -   introducing the liquid carbon dioxide stream (A) into a        distillation column (B) having packing (C) therein, and        stripping volatile impurities from the liquid carbon dioxide        stream with the packing;    -   vaporizing the liquid carbon dioxide stream (A) in a sump (D) of        the distillation column (B) for providing a carbon dioxide        vapor;    -   withdrawing from a vaporized portion (F) of carbon dioxide vapor        in the sump (D) a first vapor stream (G) vented from the        distillation column (B);    -   withdrawing from the vaporized portion (F) of the carbon dioxide        vapor in the sump (D) a second vapor portion (H) vented from the        sump into a conduit (I);    -   introducing the second vapor portion (H) in the conduit (I) into        the carbon dioxide vapor feed stream upstream of the at least        one purifying filter (13,14); and    -   introducing the carbon dioxide vapor feed stream (L) into a        distillation column (M) having packing (N) therein;    -   condensing a first portion (O) of the carbon dioxide vapor feed        stream (L) within a condenser (18) in fluid communication with        the distillation column (M) to form another intermediate liquid        carbon dioxide stream (T) and a liquid vent stream (Q); and    -   introducing the another intermediate liquid carbon dioxide        stream (T) into the receiver (20), and venting the liquid vent        stream (Q) from a bottom of the distillation column (M).

An apparatus embodiment of the present invention calls for producing apurified, pressurized liquid carbon dioxide stream, including a liquidcarbon dioxide supply tank (10) for distilling off a feed streamcomprising carbon dioxide vapor, at least one purifying filter (13,14)for purifying the carbon dioxide vapor feed stream, a condenser (18) forcondensing the carbon dioxide vapor feed stream into an intermediateliquid carbon dioxide stream, a receiver (20) for accumulating theintermediate liquid carbon dioxide stream, a high-pressure accumulationchamber (30) for accepting the intermediate liquid carbon dioxide streamfrom the receiver (20), a heater (31) for heating the high-pressureaccumulation chamber (30) for pressurizing the carbon dioxide liquidcontained therein to a delivery pressure, a sensor (45) for detectingwhen the high-pressure accumulation chamber (30) requires replenishmentof liquid carbon dioxide (10), a flow network having conduits connectingthe bulk supply tank, the condenser, the receiver and the high-pressureaccumulation chamber and for discharging the pressurized liquid carbondioxide stream therefrom, the conduits of said flow network including avent line (51) from the high-pressure accumulation chamber (30) to thecondenser (18) to facilitate introduction of the intermediate liquidcarbon dioxide stream into the high-pressure accumulation chamber, andthe flow network having valves associated with said conduits to allowfor isolation of components of the apparatus, wherein the improvementcomprises:

-   -   a distillation column (B) having packing (C) therein and a        sump (D) below the packing, the distillation column in fluid        communication with the liquid carbon dioxide supply tank for        receiving the liquid carbon dioxide stream and the packing        stripping volatile impurities from the liquid carbon dioxide        stream;    -   a heater (E) in contact with the liquid carbon dioxide stream in        the sump (D) for vaporizing the liquid carbon dioxide stream in        the sump;    -   a vent in the distillation column (B) from which a first        vaporized portion (G) of carbon dioxide vapor in the sump (D) is        withdrawn from the distillation column: and    -   a conduit (I) in fluid communication with the sump (D) and from        which a second vaporized portion (H) of the carbon dioxide vapor        in the sump is withdrawn into the conduit (I) to be introduced        into the carbon dioxide vapor feed stream.

Still another apparatus embodiment of the present invention calls for anapparatus for producing a purified, pressurized liquid carbon dioxidestream, comprising: a distillation column (B) having packing (C) thereinand a sump (D) below the packing, the distillation column in fluidcommunication with the liquid carbon dioxide supply tank for receivingthe liquid carbon dioxide stream and the packing stripping volatileimpurities from the liquid carbon dioxide stream; a heater (E) incontact with the liquid carbon dioxide stream in the sump (D) forvaporizing the liquid carbon dioxide stream in the sump; a vent in thedistillation column (B) from which a first vaporized portion (G) ofcarbon dioxide vapor in the sump (D) is withdrawn from the distillationcolumn: and a conduit (I) in fluid communication with the sump (D) andfrom which a second vaporized portion (H) of the carbon dioxide vapor inthe sump is withdrawn into the conduit (I) to be introduced into thecarbon dioxide vapor feed stream.

Still another apparatus embodiment of the present invention calls for inan apparatus for producing a purified, pressurized liquid carbon dioxidestream, including a liquid carbon dioxide supply tank (10) fordistilling off a feed stream comprising carbon dioxide vapor, at leastone purifying filter (13,14) for purifying the carbon dioxide vapor feedstream, a condenser (18) for condensing the carbon dioxide vapor feedstream into an intermediate liquid carbon dioxide stream, a receiver(20) for accumulating the intermediate liquid carbon dioxide stream, ahigh-pressure accumulation chamber (30) for accepting the intermediateliquid carbon dioxide stream from the receiver (20), a heater (31) forheating the high-pressure accumulation chamber (30) for pressurizing thecarbon dioxide liquid contained therein to a delivery pressure, a sensor(45) for detecting when the high-pressure accumulation chamber (30)requires replenishment of liquid carbon dioxide (10), a flow networkhaving conduits connecting the bulk supply tank, the condenser, thereceiver and the high-pressure accumulation chamber and for dischargingthe pressurized liquid carbon dioxide stream therefrom, the conduits ofsaid flow network including a vent line (51) from the high-pressureaccumulation chamber (30) to the condenser (18) to facilitateintroduction of the intermediate liquid carbon dioxide stream into thehigh-pressure accumulation chamber, and the flow network having valvesassociated with said conduits to allow for isolation of components ofthe apparatus, wherein the improvement comprises:

-   -   a distillation column (M) having packing (N) therein for        receiving the carbon dioxide vapor feed stream (L) therein;    -   a condenser (18) in fluid communication with the distillation        column (M) for condensing a first portion (O) of the carbon        dioxide vapor feed stream (L) within the condenser to form        another intermediate liquid carbon dioxide stream (T) and a        liquid vent stream (Q); and    -   a receiver (20) for receiving the another intermediate liquid        carbon dioxide stream (T) into the receiver, and an outlet in        the distillation column (M) through which is vented the liquid        vent stream (Q).

Still another apparatus embodiment of the present invention calls for asapparatus for producing a purified, pressurized liquid carbon dioxidestream, comprising: a distillation column (M) having packing (N) thereinfor receiving the carbon dioxide vapor feed stream (L) therein; acondenser (18) in fluid communication with the distillation column (M)for condensing a first portion (O) of the carbon dioxide vapor feedstream (L) within the condenser to form another intermediate liquidcarbon dioxide stream (T) and a liquid vent stream (Q); and a receiver(20) for receiving the another intermediate liquid carbon dioxide stream(T) into the receiver, and an outlet in the distillation column (M)through which is vented the liquid vent stream (Q).

Still another apparatus embodiment of the present invention calls for anapparatus for producing a purified, pressurized liquid carbon dioxidestream, including a liquid carbon dioxide supply tank (10) fordistilling off a feed stream comprising carbon dioxide vapor, at leastone purifying filter (13,14) for purifying the carbon dioxide vapor feedstream, a condenser (18) for condensing the carbon dioxide vapor feedstream into an intermediate liquid carbon dioxide stream, a receiver(20) for accumulating the intermediate liquid carbon dioxide stream, ahigh-pressure accumulation chamber (30) for accepting the intermediateliquid carbon dioxide stream from the receiver (20), a heater (31) forheating the high-pressure accumulation chamber (30) for pressurizing thecarbon dioxide liquid contained therein to a delivery pressure, a sensor(45) for detecting when the high-pressure accumulation chamber (30)requires replenishment of liquid carbon dioxide (10), a flow networkhaving conduits connecting the bulk supply tank, the condenser, thereceiver and the high-pressure accumulation chamber and for dischargingthe pressurized liquid carbon dioxide stream therefrom, the conduits ofsaid flow network including a vent line (51) from the high-pressureaccumulation chamber (30) to the condenser (18) to facilitateintroduction of the intermediate liquid carbon dioxide stream into thehigh-pressure accumulation chamber, and the flow network having valvesassociated with said conduits to allow for isolation of components ofthe apparatus, wherein the improvement comprises:

-   -   a distillation column (B) having packing (C) therein and a        sump (D) below the packing, the distillation column in fluid        communication with the liquid carbon dioxide supply tank for        receiving the liquid carbon dioxide stream and the packing        stripping volatile impurities from the liquid carbon dioxide        stream;    -   a heater (E) in contact with the liquid carbon dioxide stream in        the sump (D) for vaporizing the liquid carbon dioxide stream in        the sump;    -   a vent in the distillation column (B) from which a first        vaporized portion (G) of carbon dioxide vapor in the sump (D) is        withdrawn from the distillation column:    -   a conduit (I) in fluid communication with the sump (D) and from        which a second vaporized portion (H) of the carbon dioxide vapor        in the sump is withdrawn into the conduit (I) to be introduced        into the carbon dioxide vapor feed stream; and    -   a distillation column (M) having packing (N) therein for        receiving the carbon dioxide vapor feed stream (L) therein;    -   a condenser (18) in fluid communication with the distillation        column (M) for condensing a first portion (O) of the carbon        dioxide vapor feed stream (L) within the condenser to form        another intermediate liquid carbon dioxide stream (T) and a        liquid vent stream (Q); and    -   a receiver (20) for receiving the another intermediate liquid        carbon dioxide stream (T) into the receiver, and an outlet in        the distillation column (M) through which is vented the liquid        vent stream (0).

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present inventive embodiments,reference may be had to the following detailed description taken inconnection with the accompanying drawing Figures, of which:

FIG. 1 is a schematic view of a first embodiment of an apparatus in asystem for carrying out a first embodiment of a process according to thepresent invention;

FIG. 2 is a schematic view of a second embodiment of an apparatus in thesystem for carrying out a second embodiment of a process according tothe present invention;

FIG. 3 is a schematic view of an enlarged portion of the secondembodiment shown in FIG. 2; and

FIG. 4 is a schematic view of the first and second embodiments in thesystem for carrying out the first and second embodiments according tothe present invention.

DETAILED DESCRIPTION

An apparatus and process are provided including introducing a feedstream comprising carbon dioxide vapor into a purifying filter, such asfor carrying out gas phase purification; condensing the purified CO₂stream, such as by use of mechanical refrigeration or cryogenicrefrigerants; isolating the high purity liquid CO₂; and, vaporizing aportion of the liquid CO₂, such as by using a heater element, to achievethe target pressure.

In one embodiment, the apparatus and process operating cycle is designedto maintain a continuous supply of high-pressure pure liquid carbondioxide for a period up to about 16 hours, with about 8 hours to resetthe system, that is, to replenish the high purity liquid carbon dioxideavailable for delivery. An example of the operating cycle andcorresponding “Modes”, and the logic controlling the cycle of the systemis presented below in Table 1.

By way of example, in one embodiment, gaseous carbon dioxide iswithdrawn from a bulk tank of liquid carbon dioxide, where single stagedistillation purification occurs, removing a majority of the condensablehydrocarbons. From the bulk tank, the gaseous carbon dioxide passesthrough a coalescing filter, providing a second level of purification.The gaseous carbon dioxide is re-condensed in a low-pressureaccumulator, providing the third level of purification by removing thenon-condensable hydrocarbons. The low-pressure liquid is thentransferred to a high-pressure accumulator. Once filled, an electricheater pressurizes the accumulator up to the desired pressure set-point.Upon reaching the pressure set point, the accumulator enters Ready mode(Mode 4, as in Table 1). In one embodiment, the process maintains highpurity liquid carbon dioxide to the point of use for a period of up toabout 16 hours. After the liquid has been expended, the system mayreturn to Mode 1 and repeat the operating sequence.

With reference to FIGS. 1 and 2, a carbon dioxide purification andsupply system is shown generally at 1 and 2. From a bulk supply ofliquid carbon dioxide 10, a feed stream 11 comprising carbon dioxidevapor is distilled in a first purification stage, and is introduced intoa purifying particle filter 13 and a coalescing filter 14 which can beany of a number of known, commercially available filters, for a secondstage purification. Valves 12 and 15 are provided to isolate thepurifying filter(s) 13,14. The bulk supply may be a tank of liquid CO₂maintained at about 300 psig (2.1 MPa) and about 0° F. (−18° C.). Ascarbon dioxide vapor is drawn out of the bulk supply tank, a portion ofthe liquid carbon dioxide in the bulk tank is drawn through conduit 16and introduced to a pressure build device 17 such as an electric orsteam vaporizer or the like, to maintain the pressure relativelyconstant within the bulk supply tank even though carbon dioxide vapor isbeing removed. The vaporizer takes liquid CO₂ from the supply tank anduses heat to change the CO₂ from the liquid phase to the gas phase. Theresulting CO₂ gas is introduced back into the headspace of the supplytank.

The feed stream 11 after having been purified in the second stage isintroduced into a condenser 18 that is provided with a heat exchanger 21to condense the carbon dioxide vapor into a liquid 19. Such condensationis effected by an external refrigeration unit 22 that circulates arefrigeration stream through the heat exchanger, preferably of shell andtube design. Isolation valves 28 and 29 can be provided to isolaterefrigeration unit 22 and its refrigerant feed line 26 and return line27. The liquid carbon dioxide 19 is temporarily stored in a receivervessel 20, that is, a low pressure accumulator. The level of liquid inthe receiver vessel 20 is controlled by a level sensor 44 (such as alevel differential pressure transducer) and pressure sensor 54 (such asa pressure transducer) via a controller (not shown), such as aprogrammable logic computer.

An intermediate liquid stream comprising high purity CO₂ liquid 24 isintroduced from the receiver vessel 20 into a high-pressure accumulationchamber 30. The high-pressure accumulation chamber 30 is heated, forexample, by way of an electrical heater 31, to pressurize the liquid toa delivery pressure of the pressurized liquid carbon dioxide stream tobe produced by the system 1.

An insulation jacket 23, such as formed of polyurethane or theequivalent, can be disposed about the condenser 18, the conduit forcarrying the liquid CO₂ 19, the high pressure accumulation vessel 30,and the outlet conduit 32 and associated valves to maintain the desiredtemperature of the liquid CO₂.

A valve network controls the flow within the system 1. In this regard,fill control valve 25 controls the flow of the intermediate liquidstream from the receiver vessel 20 to the high-pressure accumulationchamber 30. Control of the flow of the high pressure liquid carbondioxide through outlet conduit 32 is effected by product control valve34. Drain valve 33 also is connected to outlet conduit 32 for samplingor venting, as needed. The venting of the high-pressure accumulationchamber 30 via vent line (conduit) 51 to the condenser 18 is controlledby vent control valve 52. A pressure relief line 55 from the condenser18 to the receiver vessel 20 passes vapor from the receiver vessel 20back to the condenser 18 as liquid carbon dioxide 19 enters the receivervessel 20.

A pressure sensor 53 (such as a pressure transducer) monitors thepressure and a level sensor 45 (such as a level differential pressuretransducer) monitors the level of liquid carbon dioxide within thehigh-pressure accumulation chamber 30 in order to control the heater 31for vaporizing a portion of the liquid carbon dioxide, so that a desiredpressure of the liquid carbon dioxide can be supplied therefrom. Atemperature sensor (not shown) can monitor the liquid carbon dioxidetemperature in the heater 31 or accumulation chamber 30.

The process has six operating sequences, or modes, for the high-pressurecarbon dioxide accumulator (AC-1). The cycle logic controls the valves,heaters and refrigeration according to these modes. Table 1 lists thepossible operation modes.

TABLE 1 1. High-Pressure Accumulator Status Modes. Mode DesignationDescription Offline 0 All valves closed, heaters off, refrigeration off.Vent 1 Depressurize accumulator 30 prior to refilling with low- pressureliquid. Vent valve 52 open. Fill valve 25 and product valve 34 closed.Refrigeration on. Fill 2 Filling accumulator 30 with low-pressureliquid. Vent valve 52 and fill valve 25 open. Product valve 34 closed.Refrigeration on. Pressurize 3 Pressurizing accumulator 30 up to the setpoint (i.e. using electric immersion heater 31). Vent, fill and productvalves closed. Ready 4 System hold at pressure awaits dispensing highpressure liquid. Vent, fill and product valves closed. Online 5 Systemsupplying high-pressure liquid. Product valve 34 open. Vent valve 52 andfill valve 25 closed.

High pressure carbon dioxide from the high pressure accumulator travelsthrough outlet conduit 32 and may be again purified in a furtherpurification stage by one of two particle filters 41 and 42. Theparticle filters 41 and 42 can be isolated by valves 35,36 and 37,38respectively, so that one filter can be operational while the other isisolated from the conduit by closure of its respective valves, forcleaning or replacement. The high pressure, purified liquid carbondioxide stream 43 emerges from the final filtration stage for use in thedesired process, such as cleaning of optic elements.

The optical component to be processed is contacted with high purity CO₂directly in a cleaning chamber, such that the contamination residue isdissolved and dislodged by the CO₂. The liquid CO₂ may be supplied tothe cleaning chamber at about 700 psig to about 950 psig (4.8 MPa to 6.6MPa) or higher.

When the high-pressure accumulation chamber 30 is near empty, as sensedby level sensor 45 and/or the pressure sensor 53, vent control valve 52opens to vent he high-pressure accumulation chamber. Fill control valve25 opens to allow intermediate liquid stream 24 to fill thehigh-pressure accumulation chamber 30. When the differential pressuresensor indicates the completion of the filling, control valves 25 and 52close, and the liquid carbon dioxide is heated by electrical heater 31to again pressurize the liquid within the high-pressure accumulationchamber 30.

Pressure relief valves 46,47,48 may be provided for safety purposes, inconnection with the high-pressure accumulation chamber 30, receivervessel 20, and condenser 18, respectively.

Referring again to FIG. 1, another embodiment of the system 1 includesan apparatus 100 for controlling and removing relatively lighterimpurities (such as those having a boiling point less than CO₂, forexample N₂, H₂ or O₂) from the liquid CO₂ stream, which apparatusincludes a conduit “A” connected to a bottom of the bulk storage tankhaving the liquid carbon dioxide 10 therein, and in fluid communicationwith the liquid CO₂. The liquid CO₂ is removed as a feed stream from thetank through the conduit A and introduced into an inlet of adistillation column “B” having packing “C” therein. The liquid CO₂ flowsdownward along an interior of the column B and through the packing Cinto a sump “D” of the column, where a heater “E” is disposed near abottom of the sump. The liquid CO₂ is vaporized by the heater E, wherebya portion “F” of the vaporized CO₂ rises through the packing C as avapor stream “G” to remove the lighter impurities from the stream andthereafter be vented to the atmosphere as shown in FIG. 1. Another ofthe vapor portion F is exhausted as a vapor stream “H” through a conduit“I”, the conduit I having one end in fluid communication with the sump Dand another end “J” in fluid communication with the valve 12.

Another exemplary embodiment of an apparatus according to the presentinvention is shown generally at FIG. 2. Elements shown in FIG. 2 whichcorrespond to the elements described above with respect to FIG. 1 havebeen designated by corresponding reference numbers. The elements of FIG.2 are designed for use in the same manner as those shown in FIG. 1,unless otherwise stated.

With reference to FIG. 2, an alternative impurity control for a highpressure carbon dioxide purification and supply system is showngenerally at 2. From a bulk supply of liquid carbon dioxide 10, a feedstream 11 comprising carbon dioxide vapor is distilled in a firstpurification stage, and is introduced into a purifying particle filter13 and a coalescing filter 14 which can be any of a number of known,commercially available filters, for a second stage purification. Valves12 and 15 are provided to isolate the purifying filter(s) 13,14.

The feed stream 11 after having been purified in the second stage isintroduced into the receiver vessel 20 that is provided with a heatexchanger 21 to condense the carbon dioxide vapor into a liquid, Suchcondensation is effected by an external refrigeration unit 22 thatcirculates a refrigeration stream through the heat exchanger, preferablyof shell and tube design. Isolation valves 28 and 29 can be provided toisolate refrigeration unit 22 and its refrigerant feed line 26 andreturn line 27. The liquid carbon dioxide is temporarily stored in thereceiver vessel 20, that is, a low pressure accumulator.

As may be appreciated, since vapor is being condensed within receiver20, a separation of any impurities present within the vapor might beeffected by which the more volatile impurities would remain inuncondensed vapor and less volatile impurities would be condensed intothe liquid. Although not illustrated, sample lines may be connected tothe receiver vessel 20 for sampling and drawing off liquid and vapor asnecessary to lower impurity concentration within the receiver.

An intermediate liquid stream comprising high purity liquid 24 isintroduced into first and second pressure accumulation chambers 30 a and30 b. First and second pressure accumulation chambers 30 a and 30 b areheated, preferably by way of electrical heater 31, to pressurize theliquid to a delivery pressure of the pressurized liquid carbon dioxidestream to be produced by apparatus 2.

A valve network controls the flow within the system. In this regard,fill control valve 25 controls the flow of the intermediate liquidstream from the receiver 20 to the high-pressure accumulation chambers30 a and 30 b. Control of the flow of the high pressure liquid carbondioxide through outlet conduit 32 is effected by product control valve34. Drain valve 33 also is connected to outlet conduit 32 for samplingor venting, as desired. The venting of the high-pressure accumulationchamber 30 via vent line (conduit) 51 to the condenser 18 is controlledby vent control valve 52.

First and second high pressure accumulation chambers 30 and 30 b may beinterconnected by conduit 39 without an isolation valve interposed therebetween, so that both act effectively as a single unit, at lower cost.

A pressure sensor 53 (such as a pressure transducer) monitors thepressure and a level sensor 45 (such as a level differential pressuretransducer) monitors the level of liquid carbon dioxide within thehigh-pressure accumulators 30 a and 30 b in order to control the heater31 for vaporizing a portion of the liquid carbon dioxide, so that adesired pressure of the liquid carbon dioxide can be supplied therefrom.

High pressure carbon dioxide from the high pressure accumulator travelsthrough outlet conduit 32 and is again purified in a furtherpurification stage by one of two particle filters 41 and 42. Theparticle filters 41 and 42 can be isolated by valves 35,36 and 37,38,respectively, so that one filter can be operational while the other isisolated from the conduit by closure of its respective valves, forcleaning or replacement. The high pressure, purified liquid carbondioxide stream 43 emerges from the final filtration stage for use in thedesired process as described above. When the requirement for thepurified carbon dioxide stream 43 is no longer needed, or can no longerbe met, the apparatus begins a replenishment cycle. That is, after Mode5 is complete, the system can return sequentially to Mode 1, Mode 2, andsoon, as set forth in Table I.

Further features of the system and process include a fully automatedmicroprocessor controller which continuously monitors system operationproviding fault detection, pressure control and valve sequencing,ensuring purifier reliability, while minimizing operator involvement. Byway of example and not limitation, level sensors 44,45, pressure sensors53,54, and temperature sensors can provide infom1ation for thecontroller, in order to provide instructions to flow control valves15,34,52, or pressure relief valves 46,47,48. The valves in the systemmay be actuated pneumatically, by pulling a tap off of the CO₂ vaporconduit such as at valve 57, to supply gas for valve actuation.

Referring to FIGS. 2 and 3 there is shown another embodiment of anapparatus 200 for controlling and removing relatively heavier impurities(having a boiling point greater than CO₂, for example, water, methanolor ethanol) from the liquid CO₂ stream in the system 2. The apparatusembodiment 200, generally, reconfigures the vapor feed. That is, insteadof feeding the vaporized CO₂ directly to the condenser 18, the CO₂ vaporis directed to a distillation column arranged between the condenser 18and the receiver vessel 20. In this embodiment, CO₂ vapor rises throughthe distillation column and is condensed in the condenser 18. A portionof the condensed CO₂ runs back down through the column and washes outthe heavier impurities from the vapor stream so that the heavierimpurities are purged from a bottom of the column. A remaining condensedportion of the CO₂ bypasses the column and is sent to the receivervessel.

In particular, and referring also to the apparatus 200 shown in FIG. 3,the CO₂ vapor feed stream 11 downstream of the coalescing filter 14 isprovided into a conduit “L”. The feed stream 11 contains trace amountsof heavy impurities. The conduit L is connected to and in fluidcommunication with an inlet at a bottom of a distillation column “M”. Avapor-liquid contact material “N”, such as for example structuredpacking or random packing, is disposed at an interior of the column M.The feed stream vapor travels upward at an interior of the column Mthrough the packing N. A first portion “O” of the vapor enters thecondenser 18 where the vapor is condensed. The resulting condensedliquid “P” returns to the column M, whereupon such liquid runs down thepacking N and is in countercurrent contact with the uprising first vaporportion O. This condensed liquid washes out heavy impurities in theuprising vapor portion O and forms an impurity laden liquid stream “Q”that is purged from the column M through an outlet at a bottom of thecolumn into a conduit “R”, whereupon the stream Q is vented to theatmosphere. A second portion “S” of the liquid from the condensed liquidP, which is now free of the heavy impurities, is removed from a top ofthe distillation column M and sent through a conduit “T” to an inlet ofthe receiver vessel 20.

FIG. 4 shows the apparatus embodiments 100,200 incorporated into, forexample, the system 2 of FIG. 2 to remove both lighter and heavierimpurities from a liquid CO₂ feed stream. It is understood however thatthe apparatus embodiments 100,200 can also be incorporated into thesystem 1 of FIG. 1 to remove both lighter and heavier impurities from aliquid CO₂ feed stream.

The systems 1,2 and the apparatus embodiments 100,200 above may includesystem alarms to detect potential hazards, such as temperature orpressure excursions, to ensure system and apparatus integrity. Alarm andwarning conditions may be indicated at the operator interface and may beaccompanied by an alarm beeper. A human machine interface displays valveoperation, operating mode, warning and alarm status, sequence timers,system temperature and pressure, heater power levels, and system andapparatus cycle count.

In summary, industrial grade CO₂ gas may be pulled off of the head spaceof a supply tank, where the supply tank acts as a single stagedistillation column (Stage 1). The higher purity gas phase is passedthrough at least a coalescing filter, reducing the condensablehydrocarbon concentration and resulting in a higher level of purity(Stage 2). Stage 3 includes a mechanical or cryogenic refrigerationsystem to effect a phase change from the gas phase back to the liquidphase. All non-condensable hydrocarbons and impurities are thus removedfrom the operative carbon dioxide liquid stream.

The subject apparatus 100,200 and related processes of same permitcyclic operation of the process, rather than continuous feed operation.The apparatus and processes are also of a more economical design (byapproximately half) due to the reduction from continuous or multi-batchto single batch operation. The apparatus and processes are further of amore economical design than prior art systems, due to the omission ofaccessory equipment like boilers and condensers. The reduced footprintallows for the apparatus embodiments to be located closer to the pointof use, resulting in reduced liquid carbon dioxide boil-off.

It will be understood that the embodiment(s) described herein is/aremerely exemplary and that a person skilled in the art may make manyvariations and modifications without departing from the spirit and scopeof the invention. All such variations and modifications are intended tobe included within the scope of the invention as described and claimedherein. It should be understood that the embodiments described above arenot only in the alternative, but can be combined.

What is claimed is:
 1. In an apparatus for producing a purified,pressurized liquid carbon dioxide stream, including a liquid carbondioxide supply tank (10) for distilling off a feed stream comprisingcarbon dioxide vapor, at least one purifying filter (13,14) forpurifying the carbon dioxide vapor feed stream, a condenser (18) forcondensing the carbon dioxide vapor feed stream into an intermediateliquid carbon dioxide stream, a receiver (20) for accumulating theintermediate liquid carbon dioxide stream, a high-pressure accumulationchamber (30) for accepting the intermediate liquid carbon dioxide streamfrom the receiver (20), a heater (31) for heating the high-pressureaccumulation chamber (30) for pressurizing the carbon dioxide liquidcontained therein to a delivery pressure, a sensor (45) for detectingwhen the high-pressure accumulation chamber (30) requires replenishmentof liquid carbon dioxide (10), a flow network having conduits connectingthe bulk supply tank, the condenser, the receiver and the high-pressureaccumulation chamber and for discharging the pressurized liquid carbondioxide stream therefrom, the conduits of said flow network including avent line (51) from the high-pressure accumulation chamber (30) to thecondenser (18) to facilitate introduction of the intermediate liquidcarbon dioxide stream into the high-pressure accumulation chamber, andthe flow network having valves associated with said conduits to allowfor isolation of components of the apparatus, wherein the improvementcomprises: a distillation column (B) having packing (C) therein and asump (D) below the packing, the distillation column in fluidcommunication with the liquid carbon dioxide supply tank for receivingthe liquid carbon dioxide stream and the packing stripping volatileimpurities from the liquid carbon dioxide stream; a heater (E) incontact with the liquid carbon dioxide stream in the sump (D) forvaporizing the liquid carbon dioxide stream in the sump; a vent in thedistillation column (B) from which a first vaporized portion (G) ofcarbon dioxide vapor in the sump (D) is withdrawn from the distillationcolumn: and a conduit (I) in fluid communication with the sump (D) andfrom which a second vaporized portion (H) of the carbon dioxide vapor inthe sump is withdrawn into the conduit (I) to be introduced into thecarbon dioxide vapor feed stream.
 2. The apparatus of claim 1, furthercomprising a particle filter connected to a flow network for theapparatus to filter the pressurized liquid carbon dioxide stream.
 3. Theapparatus of claim 1, wherein the condenser (18) further comprises anexternal refrigeration circuit (22) and a heat exchanger (21) tocondense the vapor feed stream through indirect heat exchange with arefrigerant stream.
 4. The apparatus of claim 1, wherein the condenser(18) is integral with the receiver (20).
 5. The apparatus of claim 1,further comprising a heater (31) comprises an electrical heater for thehigh-pressure accumulation chamber (30).
 6. The apparatus of claim 1,wherein the at least one purifying filter (13,14) for the carbon dioxidevapor feed stream is a filter selected from the group consisting of acoalescing filter and particle filter.
 7. The apparatus of claim 1,wherein the sensor is selected from the group consisting of a levelsensor and a pressure sensor.
 8. In an apparatus for producing apurified, pressurized liquid carbon dioxide stream, including a liquidcarbon dioxide supply tank (10) for distilling off a feed streamcomprising carbon dioxide vapor, at least one purifying filter (13,14)for purifying the carbon dioxide vapor feed stream, a condenser (18) forcondensing the carbon dioxide vapor feed stream into an intermediateliquid carbon dioxide stream, a receiver (20) for accumulating theintermediate liquid carbon dioxide stream, a high-pressure accumulationchamber (30) for accepting the intermediate liquid carbon dioxide streamfrom the receiver (20), a heater (31) for heating the high-pressureaccumulation chamber (30) for pressurizing the carbon dioxide liquidcontained therein to a delivery pressure, a sensor (45) for detectingwhen the high-pressure accumulation chamber (30) requires replenishmentof liquid carbon dioxide (10), a flow network having conduits connectingthe bulk supply tank, the condenser, the receiver and the high-pressureaccumulation chamber and for discharging the pressurized liquid carbondioxide stream therefrom, the conduits of said flow network including avent line (51) from the high-pressure accumulation chamber (30) to thecondenser (18) to facilitate introduction of the intermediate liquidcarbon dioxide stream into the high-pressure accumulation chamber, andthe flow network having valves associated with said conduits to allowfor isolation of components of the apparatus, wherein the improvementcomprises: a distillation column (M) having packing (N) therein forreceiving the carbon dioxide vapor feed stream (L) therein; a condenser(18) in fluid communication with the distillation column (M) forcondensing a first portion (O) of the carbon dioxide vapor feed stream(L) within the condenser to form another intermediate liquid carbondioxide stream (T) and a liquid vent stream (Q); and a receiver (20) forreceiving the another intermediate liquid carbon dioxide stream (T) intothe receiver, and an outlet in the distillation column (M) through whichis vented the liquid vent stream (Q).
 9. The apparatus of claim 8,further comprising a particle filter connected to a flow network for theapparatus to filter the pressurized liquid carbon dioxide stream. 10.The apparatus of claim 8, wherein the condenser (18) further comprisesan external refrigeration circuit (22) and a heat exchanger (21) tocondense the vapor feed stream through indirect heat exchange with arefrigerant stream.
 11. The apparatus of claim 8, wherein the condenser(18) is integral with the receiver (20).
 12. The apparatus of claim 8,further comprising a heater (31) comprises an electrical heater for thehigh-pressure accumulation chamber (30).
 13. The apparatus of claim 8,wherein the at least one purifying filter (13,14) for the carbon dioxidevapor feed stream is a filter selected from the group consisting of acoalescing filter and particle filter.
 14. The apparatus of claim 8,wherein the sensor is selected from the group consisting of a levelsensor and a pressure sensor.
 15. In an apparatus for producing apurified, pressurized liquid carbon dioxide stream, including a liquidcarbon dioxide supply tank (10) for distilling off a feed streamcomprising carbon dioxide vapor, at least one purifying filter (13,14)for purifying the carbon dioxide vapor feed stream, a condenser (18) forcondensing the carbon dioxide vapor feed stream into an intermediateliquid carbon dioxide stream, a receiver (20) for accumulating theintermediate liquid carbon dioxide stream, a high-pressure accumulationchamber (30) for accepting the intermediate liquid carbon dioxide streamfrom the receiver (20), a heater (31) for heating the high-pressureaccumulation chamber (30) for pressurizing the carbon dioxide liquidcontained therein to a delivery pressure, a sensor (45) for detectingwhen the high-pressure accumulation chamber (30) requires replenishmentof liquid carbon dioxide (10), a flow network having conduits connectingthe bulk supply tank, the condenser, the receiver and the high-pressureaccumulation chamber and for discharging the pressurized liquid carbondioxide stream therefrom, the conduits of said flow network including avent line (51) from the high-pressure accumulation chamber (30) to thecondenser (18) to facilitate introduction of the intermediate liquidcarbon dioxide stream into the high-pressure accumulation chamber, andthe flow network having valves associated with said conduits to allowfor isolation of components of the apparatus, wherein the improvementcomprises: a distillation column (B) having packing (C) therein and asump (D) below the packing, the distillation column in fluidcommunication with the liquid carbon dioxide supply tank for receivingthe liquid carbon dioxide stream and the packing stripping volatileimpurities from the liquid carbon dioxide stream; a heater (E) incontact with the liquid carbon dioxide stream in the sump (D) forvaporizing the liquid carbon dioxide stream in the sump; a vent in thedistillation column (B) from which a first vaporized portion (G) ofcarbon dioxide vapor in the sump (D) is withdrawn from the distillationcolumn: a conduit (I) in fluid communication with the sump (D) and fromwhich a second vaporized portion (H) of the carbon dioxide vapor in thesump is withdrawn into the conduit (I) to be introduced into the carbondioxide vapor feed stream; and a distillation column (M) having packing(N) therein for receiving the carbon dioxide vapor feed stream (L)therein; a condenser (18) in fluid communication with the distillationcolumn (M) for condensing a first portion (O) of the carbon dioxidevapor feed stream (L) within the condenser to form another intermediateliquid carbon dioxide stream (T) and a liquid vent stream (Q); and areceiver (20) for receiving the another intermediate liquid carbondioxide stream (T) into the receiver, and an outlet in the distillationcolumn (M) through which is vented the liquid vent stream (Q).
 16. Theapparatus of claim 15, further comprising a particle filter connected toa flow network for the apparatus to filter the pressurized liquid carbondioxide stream.
 17. The apparatus of claim 15, wherein the condenser(18) further comprises an external refrigeration circuit (22) and a heatexchanger (21) to condense the vapor feed stream through indirect heatexchange with a refrigerant stream.
 18. The apparatus of claim 15,wherein the condenser (18) is integral with the receiver (20).
 19. Theapparatus of claim 15, further comprising a heater (31) comprises anelectrical heater for the high-pressure accumulation chamber (30). 20.The apparatus of claim 15, wherein the at least one purifying filter(13,14) for the carbon dioxide vapor feed stream is a filter selectedfrom the group consisting of a coalescing filter and particle filter.21. The apparatus of claim 15, wherein the sensor is selected from thegroup consisting of a level sensor and a pressure sensor.